The invention relates generally to vehicular antenna mounts directional antennas and more particularly to a mounting system for a signal-locating directional antenna which is positioned centrally over the roof of a vehicle and includes a means for remotely controlling the rotational orientation of the antenna by an occupant of the vehicle without the need to provide a hole in the vehicle roof.
Signal-seeking or direction-finding antennas, referred to herein as directional antennas, are used in various applications such as radio communications and broadcast signal seeking. One important industrial application for directional antennas is the identification and location of radio frequency interference sources in power distribution systems, caused by equipment sparking. Vehicles equipped with directional antennas are used to locate sparking faults so repairs can be effected. A driver or technician in the vehicle rotates the antenna to the direction of the radio frequency emission and then drives the vehicle in the direction of the emission.
The optimal location for a directional antenna on a vehicle is centered above the roof. In that location, the antenna will generally not extend beyond the sides of the vehicle and is thus protected by the vehicle against lateral interference or damage. Heretofore, placement of the antenna in the center of the roof necessitated drilling a hole through the roof, or the provision of complex parallel-actuator linkages to control the direction of the antenna. Such systems are often difficult to install and disfigure the vehicle reducing its resale value. An example of a directional antenna mount designed to extend through a roof is shown in U.S. Pat. No. 4,663,632.
There is a need for an improved directional antenna mounting system which allows the antenna to be installed centrally on top of the roof without permanently disfiguring the vehicle. It would be particularly advantageous to provide an antenna mounting system for supporting a rotatable directional antenna on a conventional vehicular roof rack of the type used to carry objects other than antennas, such as boats, skis, luggage or the like. Such roof racks are designed for temporary, removable installation by releasably clamping onto the vehicle along the side edges of the roof. Roof racks are generally adjustable in length to fit on vehicles of different sizes. They can thus provide a very versatile base for a directional antenna.
There is also a need for an improved antenna mounting system for directional antennas which is compact and minimizes wind resistance.
Finally, it would be advantageous to provide a mounting system for a directional antenna which is controllable by a control handle which includes a means for positively indicating the direction the antenna is pointing without the need to physically observe either the antenna or the control handle.
Accordingly, an antenna mounting system is provided for supporting a rotatable antenna on a vehicle and for permitting selective rotation of the antenna about a vertical axis by an occupant of the vehicle. The mounting system comprises a support frame for mounting above the roof of the vehicle. It also comprises a mast holder supported on the frame for holding the mast of an antenna. The mast holder is rotatable about a generally vertical first axis to turn the antenna about the first axis. A direction controller, positionable adjacent a window of the vehicle, is rotatably supported on the frame for rotation about a generally vertical second axis. The controller permits an occupant of the vehicle to rotate the controller and the antenna by reaching through the vehicle window. The system also includes an endless transmission means extending between the mast holder and controller for transmitting rotary motion from the controller to the mast holder. The endless transmission means responds to changes in the rotational orientation of the controller and produces a responsive identical rotation in the mast holder.
In its preferred form, the endless transmission means of the antenna mounting system includes first and second sprockets operatively coupled together by an endless toothed drive belt. The belt extends generally horizontally between the mast holder and controller. The first sprocket is operatively connected to the mast holder and the second sprocket is operatively connected to the controller, allowing rotational movement of the controller to be duplicated in the rotational movement of the mast holder. An additional preferred feature of the invention is the inclusion of one or more tactile position indicators on the handle of the controller for indicating the rotational position of the handle. The tactile position indicators allow the rotational position of the control handle to be sensed by the person operating the antenna controller.
In one embodiment, the support frame of the antenna mounting system is an elongate tubular bar designed to be bolted to a standard vehicular roof rack of a type usually employed to carry things other than directional antennas. In another embodiment of the invention, a horizontal tubular bar on the roof rack is fitted with a rotatable mast holder and a direction controller, and the transmission drive belt is threaded through the center of the roof rack bar. Thus, in the second embodiment, the bar on the roof rack becomes the support frame of the antenna mounting system to provide a compact, economical antenna controller.